The present invention relates to improvements in optical oscillators such as laser devices, and more particularly to high input power optical oscillators with frequency doubled outputs.
Laser light in the green spectrum (0.500-0.570 micron wavelengths) is particularly useful for underwater and airborne optical communications, radar, and viewing applications. Various gases, liquids with dyes, and metal vapors are available as green laser mediums but they have unacceptably long pulsing characteristics and are not sufficiently developed to meet the demands of the aforementioned application. Solid state laser mediums are particularly desirable due to their short pulse (10-20 nanoseconds) characteristics, but there is none suitable in the green spectrum. For example, Nd:YAG and ruby are particularly popular solid state mediums, but they are in the red spectrum, i.e., 1.06.mu. and 0.6963.mu. wavelengths, respectively. One technique for obtaining a desired laser radiation is by frequency doubling the light output. See for example applicant's U.S. Pat. No. 4,068,190 which discloses a Nd:YAG laser whose output is doubled to yield green light. Dual beams of equal polarity distribution are formed within the resonator in order to provide higher level energy transfer through the doubler without thermal damage to the optical components. Even at the higher input power level, however, the doubler does not operate at peak efficiency due to the reduction in energy level at the resonator output.